Letter to James Leon Williams on Natural Variation
(S707ap: 1913/1925)

Editor Charles H. Smith's Note: A letter from Wallace to Williams dated 27 June 1913, and
printed in George Wood Clapp's book The Life and Work of James Leon Williams in 1925.
Williams had had an interview with Wallace that summer, but had not gotten around to asking
his opinion on a subject of interest to him, whether "in his opinion, the appearance of humanity
could ever have depended on the survival and variation of a single pair of ancestors." So he
wrote to Wallace soon after, and received the reply printed below. Original pagination in the
book indicated within double brackets. To link directly to this page, connect with:
http://people.wku.edu/charles.smith/wallace/S707AP.htm

[[p. 238]] It is not easy to make the ordinary reader understand such a question as to variation
as you put to me. It can perhaps be best explained by a reference to very familiar cases with
which everybody is acquainted.

Everyone who will think over the subject of variation among the men and women he sees
around him will be surprised at the wonderful differences, not only in the larger characteristics
such as height, weight or complexion, but also in every single part that can be easily observed
such as the length or shape of the head, ears, nose or eyes, the length of the legs, arms or fingers,
and especially the proportion of all or any of these parts to the others. He will find all these to
vary in a most unexpected degree and very often each one seems to be quite independent of all
the others. The result is that if you could examine a large number of any one race or variety of
man, and if the question were as to the modification by selection of any one of these numerous
characters, the whole population of that race, consisting perhaps of many millions of individuals,
could be divided into two portions consisting of those in which the particular character was
above or below the average; and although those which did not differ noticeably from the average
would be most numerous, yet those which were very considerably above or below the average
might certainly be reckoned (as I stated) at one quarter of the whole, so that nature has to select
for her purposes from this enormous number of favorable or unfavorable individuals.

As it is certain that, of all living creatures which are born every year, by far the larger
portion die without leaving offspring--i.e., in infancy or in early youth--it necessarily follows
that those which are in some way inferior or imperfect will, on the average, be those from which
the next generation is not produced. Those that survive and do leave offspring will therefore be,
on the whole, better adapted to their environment, and as almost every conceivable character
does vary in this way, there is an overwhelming amount [[p. 239]] of material to carry on a
continuous improvement as regards any beneficial change.

It is therefore absolutely inconceivable, taking the facts of variation to be as they have been
proved to be, that the course of evolution could ever have depended on a few pairs of individuals
only.

The large numbers of measurements and of observations which have been made demonstrate
that in respect of variation there is no essential difference between man and all other animals. It
is also certain that an enormous majority of animals multiply much more rapidly than does man.

Nature has everywhere in all parts of the world an overwhelming number of favorable
variations to select from and it is this immense surplusage of material, and not the chance
variation of a few individuals, which gives to her operations such a much greater certainty,
universality and power of minute adjustment than those of men.

It is therefore absolutely certain that each successive ancestral form which led to the
evolution of man did exist in such vast numbers and did offer such an amount of variation as to
give it in each case the superiority which was necessary to the successful operation of natural
selection.

It is the vast scale on which nature works that is always forgotten by objectors, and it is this
that demonstrates the complete fallacy of both the Mutationists and the Mendelians. They alike
deal only with comparatively very rare variations, the former with what are called sports, the
latter with abnormalities, which usually occur among domesticated animals or cultivated plants
and therefore cannot possibly have been the agency by which the vast scheme of evolution has
been carried on for millions of ages through the whole of the seas and lands of our globe. That
agency is the universal and conspicuous variability of every part and organ of all living things.